700r4 Lockup wiring & vac. question

Discussion in 'Transmission & Driveline Topics' started by Dogwater, Feb 5, 2012.

  1. Dogwater

    Dogwater Veteran Member

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    Dec 23, 2010
    SanAntonio Tx
    I rewired the 700r4 by deleating the temp.sw.,grounding the t.c.c. solenoid & ran the pos. wire of solenoid to term. A. Then 4th pressure sw. with 1 connection,ran that wire to term. B.Now I'm going to use a vac.sw. I got off a 83 p/u,it breaks at 7.5in vac. its normally closed like the pressure sw. is.Tested vac.sw. with light bulb gave it voltage light came on,applied vac. light went off at 7.5 vac. Same with pres. sw. gave it voltage light came on, applied air light went off.So my question is when at high vac. their is voltage going to pres. sw. & t.c.c. solenoid & locked up,low vac. no voltage & it's not locked up. That's how it works, right? Next question is what is the the correct connection for the vac. sw. Should I use the port where I had the TH350 vac.mod. connected to (manifold vac.) or to the carb. ported or unported? I found these vac.sw. on 83-85 Chevy p/u, by the brake booster mounted on the firewall.Theirs 2 different kinds,one with a square metal plate,these brake at 5in. vac., the other has a round metal plate, breaks at 7.5in. vac. F.Y.I. One more thing G.M. doesn't make them anymore, & most autoparts stores don't know what they are. Couldn't find a new one. I know TCI & PATC has them but I'm a cheap basturd.
     
  2. Dogwater

    Dogwater Veteran Member

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    Dec 23, 2010
    SanAntonio Tx
    What I don't understand is how the tcc solenoid works. I know that it blocks off fluid flow. But does it block flow when it has voltage or is it open with voltage.I know the press.sw. is only going to allow lockup in 4th.Anyone know what pressure the sw. is suppose to operate at?
     
  3. Twisted_Metal

    Twisted_Metal Moderator Staff Member Lifetime Gold Member

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    Feb 26, 2004
    Bloomington, MN
    Use manifold vacuum for the vacuuum switch.
    It should kill power to the lock-up solenoid circuit and release the converter when the throttle opens. (Vacuum drops)

    If I'm reading your desription correctly... I think you have it right.

    This is a diagram of the system I used for my 200-4R.

    [​IMG]
     
  4. Leonards78LT

    Leonards78LT Veteran Member Lifetime Gold Member

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    Jan 21, 2001
    Central Oklahoma

    When the right conditions are met (above a preset vehicle speed, transmission in top gear, brake pedal not depressed) the soleniod opens up with voltage applied and allows the fluid travel to the opening in the center of the output shaft to the specially coupling plate in the torque converter and eliminates slippage which "locks the torque converter" to engine speed, nearly a 1;1 ratio.
    When the engine speed falls below a preset speed or the brake pedal is depressed, the circuit is interrupted and the fluid passage is blocked and the torque converter plate is released, the released fluid is bled off through a checkball.
    The one way you can tell if everything is hooked up correctly, is go out to a open road where you can safely get the car to above 40-45 mph at steady cruising speed and while your foot is still on the gas, lightly depress your brake pedal and you should be able to hear a difference when the engine rpm's pick up slightly, take you foot off the break and the lock up again should engage,and engine rpm's drop, if your vehicle speed is above the preset.
    If you have the vacuum switch wired in series with the pressure switch it should disengage the TCC lock up as well.
    I hope this helps.
    I have done basically the same thing on my 200-4R and it works beautifully.
     
  5. Leonards78LT

    Leonards78LT Veteran Member Lifetime Gold Member

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    Jan 21, 2001
    Central Oklahoma

    I'm glad you found your diagram, I could not find mine that I had made. Pictures are sometimes better than words.
     
  6. Twisted_Metal

    Twisted_Metal Moderator Staff Member Lifetime Gold Member

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    Feb 26, 2004
    Bloomington, MN

    I also added an indicator light.
    Whenever the transmission is in OD and the solenoid has power.... It lights.
     
  7. Dogwater

    Dogwater Veteran Member

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    Dec 23, 2010
    SanAntonio Tx
    Thank you,I'll save this diagram on my pad. Theirs nothing like rebuilding something you don't completely understand,but I know a boatload more than I did before.I'm the kind of person that needs to see how it works in my head before I tear it apart.I blew all that off and went for it, theirs only one way to learn.Theirs still alot I don't know. Thanks
     
  8. fbody_mike

    fbody_mike Veteran Member


    It wasn't too much work (YET), but I decided to wire an indicator light to my TCC solenoid circuit because I thought it would be cool to see when the TCC is active. I have mine wired like the above circuit but the indicator light only goes on when I am accelerating in 4th gear. Crusing at say 65 mph in OD, the indictor is off untill I accelerate. I bypassed the vacuum switch to eliminate that as a cause. How does your indicator light behave?


    I think I may need a new 4th gear switch.
     
  9. Twisted_Metal

    Twisted_Metal Moderator Staff Member Lifetime Gold Member

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    Feb 26, 2004
    Bloomington, MN
    Something doesn't sound right there.

    Mine lights up as soon as it shifts to 4th gear.
    It stays lit until I step down on the throttle, hit the brakes or let the car coast down to about 25 mph where the trans downshifts itself.

    I can't accelerate with any serious intent in 4th without it dropping back to 3rd.
    The light goes off when the vacuum drops (more throttle = less vacuum) and it immediately downshifts to 3rd.
    It will downshift to 2nd at WOT if I'm only doing 45 mph or so.
     
  10. fbody_mike

    fbody_mike Veteran Member

    Replaced the 4th gear switch and now it is working as it should. The old switch might of had some debris in. I sprayed it with cleaner and was able to get it to work on the bench. Doesn't matter the new one is in the there now (got it from Bow Tie Overdrives). The indicator light is a great idea.

    By the way, ATF still tastes horrible. :screwup:
     

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